A polarizing beam splitter is an element by which incident light is split into two components, the extraordinary ray (e-ray) and the ordinary ray (o-ray) with their polarization directions perpendicular to each other and with the e-ray and o-ray emerging from the beam splitter along two directions. Such an element is widely used as a component in optical fiber communications, liquid crystal displays, optical disc systems, and other optical systems.
Conventional polarizing beam-splitters such as the polarizing prisms employ the effect of birefringence only. They are described, for example, in Handbook of Optics, Vol. II, pp. 3.19-3.26 (1995). Although prisms have high extinction ratios, high transmittance, and high optical damage thresholds, a large amount of birefringent crystal with fine optical quality must be utilized as the raw material to make them; otherwise, their aperture or beam splitting angle will be severely limited. As a result, they are large, heavy, and relatively expensive.
Another type of polarizer is a birefringence diffraction grating-type polarizer (European patent, No. 0349144 A2). In this type of polarizer, periodic proton ion-exchanged regions are provided on the principal plane surface of an optically anisotropic crystal substrate to provide an optical diffraction grating, and a dielectric layer is provided on each of the periodic proton ion-exchanged regions. The refractive index of the dielectric layer is a approximately equal to that of the crystal substrate, and the whole surface of the optical diffraction grating is covered by an anti-reflection layer of a single material having a uniform thickness. The polarizer can split a parallel incident beam into a diffracted beam of zero-order with the direction of polarization along the x-axis and a series of plus- and minus-order diffracted beams with direction of polarization along the y-axis. Because one of two polarization components of the incident light beam is diffracted into plus- and minus-orders, these polarization beams propagate in many directions. Therefore, this kind of polarizer is an imperfect polarizing beam splitter.
A polarizing beam splitter for use with monochromatic light or monochromatic long-wavelength radiation or polychromatic light is needed which can: provide a high extinction ratio with almost complete separation of the pure polarized e-ray and o-ray; provide a high transmittance, or negligible absorption; be made in thin sheet-form; have high optical damage threshold; provide the possibility of a large beam-splitting angle; be produced in quantity at low cost, especially if made from plastic and produced by replication techniques; and, be made with a large aperture and in any desired shape if formed from optical plastics.